Reconstructing Holocene seismic and tsunami history along the Rio Grande coast, Oaxaca, Mexico

This study aims to identify past earthquakes and tsunamis in the Oaxaca region of Mexico, a segment of the subduction zone between the Cocos and North American plates. We reconstructed paleoelevations from the sedimentary record using diatom-based transfer functions to identify co-seismic, post-seismic, inter-seismic, and permanent deformation associated with land-level changes. To achieve this, we developed a paleoelevation model using modern diatoms. Up to four allochthonous sand layers were identified as tsunami deposits and their triggering earthquakes, associated coseismic uplift and subsidence. Unit 1 (1769 ± 74 CE) records co-seismic uplift of 0.065 ± 1.04 m and is associated with the 1787 M8.6 earthquake and tsunami. Unite 2 (1085 ± 40 CE) records a co-seismic uplift of 0.082 ± 0.93 m. Unite 3 (830 ± 45 CE) shows a co-seismic subsidence of −0.091 ± 1.08 m. Unite 4, dated between 811 and 751 cal BC and 766–465 cal BC, records a co-seismic uplift of 0.513 ± 0.37 m, likely caused by a > M7.5 tsunamigenic earthquake. The reconstructed magnitudes, inferred from land-level changes, reveal a variable seismic history. Finally, we identified a cumulative permanent uplift deformation of 0.76 m over the last 2800 years.